Bolted Bonnet Parallel Slide Gate Valve

The name is two independent decisions sold as one. Parallel slide is the closure: two flat discs riding on flat seat rings, held in light contact by a spring and pressed onto the downstream seat by line pressure. Bolted bonnet is the joint: body and bonnet flanges drawn together by studs onto a gasket. Either can be changed without the other - the same disc set appears in pressure seal valves at Class 1500 and above, and a bolted bonnet gate valve usually carries a wedge instead.

A parallel slide gate valve buys predictable opening torque. A wedge gate valve closed on a hot line and opened cold can bind, because contraction drives the wedge deeper between the seats until the interference exceeds what the operator can break; that is thermal binding, a dimensional problem rather than a lubrication one. Two parallel discs slide across the seat face instead of into it, so opening torque does not depend on the temperature at which the valve was closed. The trade is seating force: with no wedge angle to multiply it, the seal at low differential pressure rests on spring contact until line pressure takes over, and the same geometry traps liquid in the body cavity - hence cavity pressure relief, an equalizing hole, an equalizing line or a bypass.

Bolted bonnet answers a different question: not how the valve seals but how it is repaired. Once the line is isolated the bonnet comes off in place, the gasket is changed, the studs re-torqued - worth a heavier body and a larger bonnet flange wherever valves are maintained rather than replaced. It stops scaling around Class 1500, where the bolting needed to hold a gasket against line pressure outgrows the pressure seal alternative. The pressure seal parallel slide gate valve covers that range with the same disc mechanism.

Design Standard

Design Features

1. The advanced design concept eliminates leakage due to the damage of sealing surface caused by the sundries.
2. Significant security performance in high temperature applications.
3. The parallel disc designed to absorb thermally-induced body distortion, thereby making it ideal for high temperature steam or water supply piping.
4. Spring loaded disc not only assures contact between the disc and seat, but at all positions from open to close.The sealing between the disc and the seat is guaranteed under the equilibrate force of the spring between two discs and the valve service life is extended.
5. The position indicator can easily work without reducing the yoke or stem strength.
6. The parallel slide valve is free of jamming or seizure by temperature changing. At high pressure differential, the disc is pushed to the seat of lower pressure side, thus assures the sealing between the disc and seat by the pressure differential of the medium. 

Bolted Bonnet Parallel Slide Gate Valve drawing

Material of Construction

Dimension & Weight

Gear Operation

Class 150

Class 300

Operating Torque

Pressure Seal Parallel Slide Gate Valve

Bolted Bonnet Parallel Slide Gate Valve

Flow Coefficient (CV Value)

Notes:

Larger size data available on request.

Flow coefficient Cv is the volume of water in U.S. gallons at 5℃~40℃ per minute that passes through a valve at a pressure drop of 1 Psi. Cv is typically calculated from the following formula with unit of gal/min.

where

Q = flow rate in cubic metres per hour

G = specific gravity of liquid (water=1)

△P = pressure drop across valve in bar

Performance Parameters

Note: Due to quick development of products, the data in our catalogue may be updated. GNEE reserves the right to change the design, material or specifications without prior notice and free of obligation to furnish or install such changes on products previously sold.

Valve factory

 

 

 

 

Why GNEE and How to Order

We supply this valve as a trading and manufacturing partner, not as a plant that casts every component itself. That distinction is worth stating because it changes what you should ask us: we can tell you which foundry casts the body, which shop machines the seat rings and where the API 598 tests are witnessed, and we will say so before the order rather than after.

• One-piece minimum order, so a maintenance job and a trial order are both workable
• Stock sizes in WCB and WC6 shipping in about 7 days, from Tianjin
• 18-month warranty from shipment, with gasket and stud sets held as spares
• Third-party inspection arranged to your ITP, at production stage, not after packing
• OEM nameplates and customer drawings accepted, with the drawing number referenced on the test report

To quote accurately we need eight things, and the first one is the one that most inquiries omit:

1. Closure form - parallel seat double-disc, stated in words, not left to API 600's default
2. Size and pressure class, in NPS and ASME Class rather than PN alone
3. Body material and trim, or the design temperature and medium so we can propose both
4. End connection - raised face, ring joint or butt weld - and the end-to-end length if it is a replacement
5. Bonnet joint requirement: gasket type, stud grade and whether live loading or seal weld is needed
6. Test and certificate level - API 598 with 3.1, or 3.2 with witnessing
7. Operator - handwheel, gear, electric or pneumatic, with the actuator make if already purchased
8. Destination port and required delivery date

Send those eight lines to info@gneetube.com or +86 15824687445 and you will get a drawing, a test plan and a price against the same specification, usually within 24 hours. If your order already reads API 600 without a disc form, send it as it stands: rewriting that one line before the pattern is cut is cheaper than discovering it after the valve is in the line.

FAQ

What is the difference between a bolted bonnet and a pressure seal parallel slide gate valve?

A bolted bonnet is sealed by stud preload squeezing a gasket between two flanges, so the sealing force is fixed when the joint is assembled. A pressure seal bonnet sits on a tapered seat inside the body, and line pressure drives it up into a gasket held by a retaining ring, so sealing force rises with pressure. The bolted design is the practical choice up to about Class 600 and stays usable at Class 900; from Class 1500 upward the bolting needed becomes impractically large and the pressure seal design takes over. The trade is serviceability, because a bolted joint can be opened in line after isolation and a pressure seal joint cannot.

Is a bolted bonnet parallel slide gate valve an API 600 valve?

Yes, and unlike a pressure seal valve it sits inside the standard's own scope. API 600 is titled Steel Gate Valves - Flanged and Butt-Welding Ends, Bolted Bonnets, and its scope names bolted bonnet, outside screw and yoke, rising stem, single or double gate, wedge or parallel seating and metallic seating surfaces. The 14th edition, published in May 2021, covers NPS 1 through NPS 42 and Class 150 through 2500. The pressure seal route exists in the same standard but as a separate clause, 5.5.11, which points to MSS SP-144 Style B.

Why does a purchase order that says API 600 gate valve arrive with a wedge instead of parallel discs?

Because API 600 clause 5.6.1.1 says a one-piece wedge gate, solid or flexible, shall be furnished unless otherwise specified by the purchaser, while clause 5.6.1.2 says a parallel seat double-disc gate may be furnished only when specified by the purchaser. A supplier who ships a wedge against an API 600 order is following the standard. To receive parallel discs the order has to state parallel seat double-disc gate, or parallel slide, in the specification text and not only in a drawing title, because the body guide geometry, seat rings and stem end are set at pattern stage.

What temperature can the bonnet joint take?

Less than the body, and the limit is the bolting. A216 WCB is rated to 425 °C and A217 WC6 or WC9 to 593 °C, but ASTM A193 B7 studs, the default on a Class 600 valve, are used to about 538 °C, and their allowable stress falls from 25 ksi at 400 °F to 10 ksi at 1000 °F. Between 538 °C and 593 °C the answer is A193 B16 studs with A194 grade 4 or 7 nuts, plus a ring joint gasket instead of a spiral wound one. Above 593 °C the joint, not the body, is what fails first.

Which API 598 tests does a parallel slide gate valve have to pass?

API 598 Table 1 places parallel slide gate valves in the Globe and Parallel Slide Gate column, not the plain Gate column. In that column the shell test, backseat test, low-pressure closure test and high-pressure closure test are all required across the normal size and class ranges, whereas a plain wedge gate has the high-pressure closure test as optional up to NPS 4 at Class 1500 and above NPS 4 at Class 600. A report showing only shell and low-pressure closure has not tested the valve to the column it belongs in.

What size and pressure class range do you supply?

NPS 2 to 24, Class 150, 300, 600 and 900 as standard, in A216 WCB, A217 WC6, A217 WC9, A351 CF8M and A352 LCB. Class 1500 in sizes up to NPS 12 is quoted against a drawing because the bonnet flange and stud count grow quickly. Above Class 900 we recommend the pressure seal parallel slide gate valve instead, since the bolted joint stops being the economical answer. Sizes above NPS 24 are quoted case by case.

Can the bonnet gasket be replaced in the field?

Yes, and that is the main reason to choose a bolted bonnet. Isolate and depressurise the line, unbolt the bonnet, and replace the spiral wound gasket with a new one of the same dimensions and filler. Three rules apply. Use no sealing compound on the faces, because API 600 clause 5.5.10 prohibits it. Check that the gasket does not extend past the inner edge of the bolt holes, per clause 5.5.5. And re-torque in a cross pattern to the drawing value, because uneven stud load is the usual cause of a joint that weeps on restart.

What is the difference between a parallel slide gate valve and a flat gate valve?

They are different products that are often listed under one name. A parallel slide gate valve is a power and process valve to API 600 or ASME B16.34, with two metal-seated discs, Class 150 to 900 ratings and a service ceiling fixed by body material, so 425 °C in carbon steel and 593 °C in chrome-moly. A flat gate or slab gate valve is a pipeline valve to API 6D, usually short pattern, often soft seated, commonly rated 1.0 to 2.5 MPa with a 121 °C ceiling, and built for pigging. A specification written for one cannot be quoted against the other.

What is the face-to-face dimension and can it replace an existing wedge valve?

Face-to-face and end-to-end lengths follow ASME B16.10, and a parallel slide body uses the same gate valve table as a wedge body, so a like-for-like replacement does not need the pipe spools altered. For reference, a Class 600 gate valve with flanged ends is 292 mm at NPS 2, 559 mm at NPS 6 and 1397 mm at NPS 24 in short pattern. The length changes with end connection and pattern, so order by end-to-end length rather than face-to-face, and hold plus zero minus zero on butt-weld ends because a welding gap cannot be closed with a gasket.

What documents come with each valve?

EN 10204 3.1 material certificates as standard, with EN 10204 3.2 when independent witnessing is required; the API 598 test report covering shell, backseat, low-pressure closure and high-pressure closure; a hardness report where NACE MR0175 applies; NDE records for casting repair areas; and marking to MSS SP-25 with the heat number traceable to the certificate. API 624 fugitive emission type test reports and ISO 15848-1 results are available when the order asks for them. Third-party inspection is arranged against your ITP and has to be scheduled to the production date, not after packing.

What is the minimum order quantity and lead time?

One piece is accepted, so a single valve can be bought for a maintenance job or for evaluation before a larger order. Common sizes in WCB and WC6 are held in stock and ship in about 7 days; made-to-order valves in WC9, CF8M or non-standard end connections run about 20 to 25 days plus transit from Tianjin. Class 900 in sizes above NPS 16 should be confirmed against the production schedule before the inquiry is closed.

Can the valve be supplied with a seal-welded bonnet or live-loaded bolting?

Both are available. A seal weld is a small fillet run around the bonnet flange after torque-up, used where fugitive emission limits or hydrogen service rule out any path at the joint; it is not a substitute for correct stud load and it makes the joint non-serviceable in line. Live-loaded bolting uses Belleville washers or disc springs under the nuts so that a small amount of thermal movement is absorbed instead of dropping the gasket seating stress. Specify one or the other, not both, and state it before the bonnet is machined.

Is a parallel slide gate valve suitable for throttling?

No. It is an isolation valve and should be operated fully open or fully closed. At a part-open position the two discs sit in the flow path, the seats erode and the discs can chatter, and API 600 permits a double-disc gate to remain partly in front of the seat openings even when fully open, so throttling makes a known restriction worse. Where flow control is needed, put a globe valve or a control valve in series rather than using this valve as a regulator.